1. Field of the Invention
The present invention relates to an access node (e.g., DSLAM) and method for optimizing the distribution of a multicast stream (mutlicast traffic) within a hybrid PPPoE/IPoE broadband assess network.
2. Description of Related Art
The following abbreviations are herewith defined, at least some of which are referred to in the ensuing description of the prior art and the preferred embodiment of the present invention.    AAA Authentication, Authorization and Accounting    BRAS Broadband Remote Access Server    CPE Customer Premises Equipment    DSL Digital Subscriber Line    DSLAM Digital Subscriber Line Access Multiplexer    IGMP Internet Group Management Protocol    IP Internet Protocol    IPoE IP over Ethernet    PPP Point-to-Point Protocol    PPPoE Point-to-Point Protocol over Ethernet
Telecommunication service providers have been trying to build a cost-effective broadband access network, while reusing the existing investments in DSL networks, yet without compromising on the ability to provide high bandwidth services (e.g., internet, television). Thanks to its compatibility with IP, simplicity of deployment, and price-to-performance ratio, Ethernet has been used to help build such a broadband access network. Two known Ethernet based broadband access networks and their drawbacks are described below with respect to FIGS. 1-2.
Referring to FIG. 1 (PRIOR ART), there is a block diagram that illustrates the basic components of a traditional IPoE broadband access network 100. The traditional IPoE broadband access network 100 includes multiple access nodes 102 (e.g., DSLAMs 102) which connect end-users 104 and their multicast devices/CPEs 106 to an Ethernet aggregation network 108. The Ethernet aggregation network 108 includes multiple Ethernet switches 110 (only three shown) and a multicast router 112 all of which are interconnected. The multicast router 112 is coupled to a multimedia server 114. In operation, the multimedia server 114 receives a multicast stream 116 (e.g., TV, radio) from a content provider 118. Then, the multimedia server 114 broadcasts the multicast stream 116 which passes through selected Ethernet switches 110 and selected DSLAMs 102 to the end-users 104 who requested to receive the multicast stream 116 (shown as end-users 104′). A detailed discussion about how all of these components function to distribute the multicast stream 116 to the appropriate end-users 104′ is provided next.
In particular, the end-users 104′ (only three shown) that desire to receive the multicast stream 116 need to transmit a multicast request 120 (IGMP join message 120) toward their respective DSLAMs 102′ (only three shown). Each upstream multicast request 120 contains an address of the desired multicast stream 116. And, each upstream multicast request 120 is encapsulated in IPoE. The DSLAMs 102′ snoop the IPoE encapsulated multicast requests 120 and register the particular end-user(s) 104′ who requested the multicast stream 116. In addition, the DSLAMs 102′ forward the IPoE encapsulated multicast requests 120 towards the multicast router 112. As the multicast requests 120 travel towards the multicast router 112, the Ethernet switches 110 snoop the IPoE encapsulated multicast requests 120 to determine which links 122 they need to use when they forward the downstream multicast stream 116 to the end-users 104′. This snooping is how the DSLAMs 102′ and Ethernet switches 110 can effectively distribute the multicast stream 116 (which is also encapsulated in IPoE) to the end-users 104′.
The main drawback of this topology is that IPoE is used to encapsulate the upstream multicast requests 120 and the downstream multicast stream 116. However, most service providers like to use PPPoE as their access protocol because it is in wide-spread use today and because it has a lot of inherent capabilities related to AAA and security. In response to this drawback, a hybrid PPPoE/IPoE broadband access network has been suggested by Juniper Networks and BellSouth. The hybrid PPPoE/IPoE broadband access network addresses this drawback by encapsulating the upstream multicast requests in PPPoE and encapsulating the downstream multicast stream (e.g., content) in IPoE. A detailed discussion about the hybrid PPPoE/IPoE broadband access network is provided in the following documents:                “IGMP Proxying vs Transparent Snooping: WT-101 Applicability”, DSL Forum document # dsl2004.471.00 by Jerome Moisand, Juniper Networks (Dec. 7-9, 2004).        “High level requirements for IPTV multicast delivery via PPPoE”, BellSouth's functional specification (Dec. 13, 2004).        
The contents of these documents are incorporated by reference herein.
A brief discussion about the traditional hybrid PPPoE/IPoE broadband access network 200 and it's main drawback is provided next with respect to FIG. 2 (PRIOR ART). As shown, the traditional hybrid PPPoE/IPoE broadband access network 200 includes multiple access nodes 202 (e.g., DSLAMs 202) which connect end-users 204 and their multicast devices/CPEs 206 to an Ethernet aggregation network 208. The Ethernet aggregation network 208 includes multiple Ethernet switches 210 (only three shown), a multicast router 212 and a BRAS 213 all of which are interconnected. The BRAS 213 is coupled to the Internet 215. And, the multicast router 212 is coupled to a multimedia server 214. In operation, the multimedia server 214 receives a multicast stream 216 (e.g., TV, radio) from a content provider 218. Then, the multimedia server 214 broadcasts the multicast stream 216 which passes through all of the Ethernet switches 210 and selected DSLAMs 202 to the end-users 204 who requested to receive the multicast stream 216 (shown as end-users 204′). A detailed discussion about how all of these components function to distribute the multicast stream 216 to the appropriate end-users 204′ is provided next.
In particular, the end-users 204′ (only three shown) that desire to receive the multicast stream 216 need to transmit a multicast request 220 (IGMP join message 220) toward their respective DSLAMs 202′ (only three shown). Each upstream multicast request 220 contains an address of the desired multicast stream 216. And, each upstream multicast request 220 is encapsulated in PPPoE (compare to FIG. 1). The DSLAMs 202′ snoop the PPPoE encapsulated multicast requests 220 and register their particular end-user(s) 204′ who requested the multicast stream 216. In addition, the DSLAMs 202′ transparently forward the PPPoE encapsulated multicast requests 220 through the Ethernet switches 210 towards the BRAs 213. And, the Ethernet switches 210 transparently forward the PPPoE encapsulated multicast requests 220 towards the BRAs 213 and not the multicast router 212 (which would not know what to do with PPPoE encapsulated multicast requests 220 since it does not support PPP). However, the Ethernet switches 210 cannot snoop the PPPoE encapsulated multicast requests 220.
This is a problem since the Ethernet switches 210 are not able to determine the links 222 they need to use to forward the downstream multicast stream 216 to the end-users 204′. To solve this problem, the Ethernet switches 210 flood all of their ports with the multicast stream 216 and send the multicast stream 216 on both appropriate links 222 and non-appropriate links 222′ towards all of the DSLAMs 202. This wastes bandwidth in the traditional hybrid PPPoE/IPoE broadband access network 200. In this example, the wasted bandwidth can be seen in Ethernet switch 210′ where the non-appropriate link 222′ is flooded with the downstream multicast stream 216 but there is no end-user 204′ associated with this link 222′ or with the corresponding DSLAM 202. As such, the Ethernet switches 210 do not effectively distribute the multicast stream 216 (which is encapsulated in IPoE) to the end-users 204′. This problem is solved by the present invention.